Contraception and Emergency Contraception for OPRA: Method Selection, Interactions and MCQs

When combined hormonal contraception is the wrong choice

Combined hormonal contraception (the combined oral contraceptive pill, and combined hormonal patches/rings) contains oestrogen, which carries a small but real increased risk of venous thromboembolism and, in specific patients, arterial events. Migraine WITH aura is a well-recognised reason to avoid oestrogen-containing contraception, because of an increased stroke risk in this specific combination — a non-oestrogen method (progestogen-only or non-hormonal) should be considered instead. It's worth being precise about the trigger: this concern applies specifically to migraine WITH aura, not migraine in general — migraine without aura is not, on its own, a reason to avoid combined hormonal contraception, and exam stems sometimes use that distinction deliberately. Other situations that favour avoiding combined hormonal contraception include a personal history of venous thromboembolism or significant thrombophilia, uncontrolled hypertension, smoking (particularly heavy smoking in a woman over 35), and the early postpartum period, especially in someone breastfeeding. Progestogen-only options — the progestogen-only pill, the implant, the injection or a hormonal IUD — don't carry the same oestrogen-related risk, but avoiding oestrogen doesn't automatically mean any one of these is the default answer: the most suitable progestogen-only or non-hormonal method still depends on the patient's broader circumstances (bleeding-pattern preferences, adherence, other risk factors).

Enzyme induction doesn't just affect the contraceptive pill

• Rifampicin is a potent, long-acting enzyme inducer and significantly reduces the efficacy of combined and progestogen-only hormonal contraception alike; additional non-hormonal precautions (or switching to a non-hormonal method for the duration of treatment and for a period after stopping) are the safest approach, particularly for oral methods.
• Other enzyme-inducing medicines with the same effect include several anti-epileptic drugs — carbamazepine, phenytoin, phenobarbitone (phenobarbital) and primidone — plus rifabutin and some antiretrovirals (notably ritonavir-boosted regimens). A useful habit is to ask specifically about AEDs, TB treatment and HIV treatment when taking a contraceptive or emergency-contraceptive history, rather than relying on the patient to volunteer it.
• Enzyme induction reduces the efficacy of hormonal emergency contraception too (both levonorgestrel and ulipristal) — this is frequently missed because emergency contraception is thought of as a one-off supply rather than a drug with its own interactions. For a patient who has used an enzyme inducer in the preceding 4 weeks, a copper IUD is preferred where it can be accessed and is appropriate for the patient; if a copper IUD can't be accessed, 3 mg levonorgestrel may be considered instead, although the evidence supporting this higher dose is limited. Treat this as guidance to weigh, not a rule that enzyme induction always means 'copper IUD, full stop.'
• St John's Wort, an over-the-counter herbal product, is also an enzyme inducer and is a genuinely under-recognised cause of contraceptive failure — a useful reminder that 'natural' products are not automatically interaction-free.
• Long-acting methods — the contraceptive injection and intrauterine methods — are generally considered less vulnerable to enzyme-inducer interactions than the combined pill, the progestogen-only pill or the implant, which is worth knowing when advising a patient who will be on an enzyme inducer long-term.

Missed-pill rules aren't the same for every method

The traditional (norethisterone-based) progestogen-only pill has a strict 3-hour window — a dose taken more than 3 hours late is considered a missed pill, with additional precautions required. The desogestrel-only pill has a wider 12-hour window, matching the combined pill's traditional missed-pill allowance. The drospirenone-only pill, also available in Australia, has its own 24-hour missed-pill window — wider again than desogestrel. This distinction is a common source of incorrect counselling, because pharmacists sometimes apply the 12-hour rule to every progestogen-only pill regardless of which one it is — checking which specific progestogen-only pill a patient is using (traditional, desogestrel or drospirenone) is essential before giving missed-pill advice.

Practise this topic

Matching the right method — and the right emergency contraception option — to a patient's specific risk factors and timeline is useful OPRA-style practice, because it's exactly the kind of multi-factor reasoning a real consultation requires. Practise more Therapeutics and Women's Health OPRA questions with ClinicalStem's OPRA question bank.

Choosing between levonorgestrel, ulipristal and a copper IUD for emergency contraception

Levonorgestrel emergency contraception (LNG-EC) is licensed for use up to 72 hours after unprotected intercourse, with effectiveness declining the longer the delay and also declining as body weight/BMI increases. Ulipristal acetate (UPA-EC) is licensed for a longer window, up to 120 hours (5 days), and is generally more effective than levonorgestrel, including later in the window and at higher body weight — but ulipristal's own effectiveness may also decline at very high BMI, so it isn't accurate to describe it as simply 'unaffected by weight.' Current Australian guidance uses body-weight decision thresholds — not hard pharmacological cut-offs — to guide the choice: above approximately 70 kg or a BMI above approximately 26 kg/m², ulipristal is generally preferred over levonorgestrel; above approximately 85 kg or a BMI above approximately 30 kg/m², a copper intrauterine device is generally preferred where it can be accessed in time, because its efficacy is not known to be reduced by body weight, unlike either oral option. These figures are guidance thresholds used to select between options, not exact points at which a drug 'stops working.' Where a copper IUD isn't accessible and levonorgestrel is being used in a higher-weight patient, a higher (3 mg) dose is sometimes considered, although the evidence supporting this doubled dose is limited.

Ulipristal acetate's interaction with progestogen runs in both directions

Ulipristal acetate works as a progesterone receptor modulator, so the interaction with progestogen-containing contraception isn't one-directional. AFTER taking ulipristal: starting or resuming a progestogen-containing contraceptive too soon can reduce both the contraceptive's effectiveness and, if taken close enough together, ulipristal's own effect — current guidance is to wait at least 5 days after ulipristal before starting or resuming hormonal contraception, using a barrier method for that interval. BEFORE taking ulipristal: use of a progestogen-containing medicine — including a progestogen-only emergency contraceptive pill taken for an earlier episode — in the previous 7 days can reduce ulipristal's own effectiveness. This 'before' direction is easy to miss because it's the opposite of the more commonly taught 'wait after' rule, and it matters specifically when a patient has used, or is using, another progestogen-containing method within that 7-day window.

Pharmacist supply of emergency contraception: professional obligations

In Australia, oral emergency contraception (both levonorgestrel and ulipristal) is available directly from a pharmacy without a prescription, following an appropriate pharmacist consultation. This comes with real professional obligations: confidential, non-judgemental counselling; screening for factors that change the recommendation (timing, weight/BMI, interacting medicines, recent progestogen use, and whether a copper IUD would be more appropriate); and being alert to signs of coercion or repeated need that might warrant a broader conversation about ongoing contraception or, where appropriate, safety concerns. Follow-up advice should be specific rather than a single generic rule: if the next period is more than 7 days late, or unusually light, advise a pregnancy test. If pregnancy could not be excluded at the time of the consultation — for example, unprotected intercourse earlier in the same cycle, or uncertainty about the timing of the last period — advise a pregnancy test at around 4 weeks regardless of whether the next period arrives on time.

Can emergency contraception be used more than once in the same cycle?

Yes — both levonorgestrel and ulipristal can be used more than once in the same cycle when clinically appropriate. Neither is intended as an ongoing contraceptive method, and repeated need is a good opportunity to discuss a more effective regular method.

Does body weight really affect which emergency contraception should be used?

Yes — levonorgestrel's effectiveness declines above roughly 70 kg/BMI 26, which is where ulipristal is generally preferred instead. Above roughly 85 kg/BMI 30, even ulipristal's effectiveness may decline, and a copper IUD (which isn't known to be affected by weight) is generally preferred where it can be accessed in time.

Why can't a patient restart the contraceptive pill immediately after taking ulipristal?

Ulipristal acetate is a progesterone receptor modulator, so the interaction runs both ways. AFTER taking ulipristal, starting a progestogen-containing contraceptive too soon can reduce the effectiveness of both — current guidance recommends a barrier method for at least 5 days before resuming hormonal contraception. BEFORE taking ulipristal, use of a progestogen-containing medicine in the previous 7 days can also reduce ulipristal's own effectiveness, which is worth asking about in the consultation.

What's the best emergency contraception option for someone taking an enzyme-inducing medicine?

A copper IUD is generally preferred if it can be accessed within the required timeframe, since its efficacy isn't reduced by enzyme induction. If a copper IUD isn't accessible, a higher (3 mg) dose of levonorgestrel is sometimes considered, although the evidence for this doubled dose is limited.

When should someone be advised to have a pregnancy test after emergency contraception?

If the next period is more than 7 days late, or unusually light, advise a pregnancy test. If pregnancy couldn't be excluded at the time of the consultation — for example, if unprotected intercourse occurred earlier in the same cycle — advise a pregnancy test at around 4 weeks regardless of whether the next period arrives on time.

Is St John's Wort really relevant to contraceptive counselling?

Yes — St John's Wort is an enzyme inducer and can reduce the efficacy of hormonal contraception in the same way that certain prescription medicines do, which makes it worth asking about specifically, since patients often don't think to mention an over-the-counter herbal product.